The present invention relates to programmable digital machines, particularly those machines having a read only control store (ROS) and adaptable to be used with or in peripheral data processing sub systems.
Many small programmable digital machines, such as those commonly referred to as mini-computers, as well as programmable I/O controllers, for cost reasons, use read only store (ROS) for resident control programs. Such machines may have all of the resident control programs in such ROS. Alternatively, such machines may not only have a ROS control memory but also an electrically alterable control memory. In some situations, the control memory may be writable; but the program functions are time shared such that program execution time is less than machine function execution time (hardware sequences and the like take longer than execution of the controlling program).
In such machines, cost is an overriding factor. This means that the number of electronic circuits and the number of words used in ROS or other forms of control memory should be minimized to the greatest extent possible. This factor is particularly important when large numbers of such machines are to be constructed.
In programmable machines, there is usually an executive routine sometimes referred to as "IDLESCAN" in programmable I/O controllers. This executive routine selects and initiates various object programs stored in ROS which accomplish predesignated machine functions. Such object programs and executive routines are used in normal data processing operations and for controlling peripheral device subsystems. This sequence is termed a "first mode of operation".
In addition to the operating or first mode of operation, each programmable machine usually has a diagnostic mode of operation which may be controlled from a maintenance panel usually mounted on or pluggable into the machine. Additionally, a large number of electronic circuits, manual switches, and the like, may be included in such a maintenance section. The diagnostic or maintenance mode of operation includes what is termed a "second mode of operation". In such second mode, the functions performed may be quite different than in the first mode. In some operational situations, the programmable machine may alternately operate in said first and second modes, all while under diagnostic procedures. The present invention not only enhances such diagnostic procedures, but enables a more efficient usage of selected computer programs in certain types of machines and operations.